The present invention relates to cement additives, and more particularly to wood-based cement additives designed to lighten the weight of the cement without degrading the cement.
Cement has a great many uses in construction and industry. One particular application is use of cement in the drilling industry, such as oil and gas drilling. As part of the drilling process, cementing is typically used to protect and seal the wellbore. Most commonly, cement is used to prevent water penetration into the well. Cementing can also be used to seal a lost circulation zone (an area where there is a reduction of flow within the well) or to plug an abandoned well. The process of cementing involves mixing cement, cement additives, and water to form a slurry, before pumping that mixture through the casing to the critical points.
Various types of cement additives exist, including additives aimed at reducing the weight or density of the cement. Examples of weight-reducing additives include microsilica, diatomaceous earth, glass spheres, and foam cement. These additives have a lower specific gravity than that of cement, which typically has a specific gravity of around 3.15 for portland cement, and thus give the cement slurry a lower density (except in the case of microsilica). Reducing the density of cement slurries leads to reduced hydrostatic pressure of the fluid column during cement placement and increased slurry yield, which reduces the amount of cement required to produce a given volume. Existing weight-reducing cement additives, however, do not come without limitations. Microspheres, or hollow glass spheres, for example, are susceptible to crushing during mixing and pumping, which may lead to increased slurry density and viscosity, decreased slurry volume, or premature slurry dehydration. Microsilica, or silica fume, is useful to improve the compressive strength, bond strength, and abrasion resistance of cement; however, it is expensive and is limited by a lack of sufficient supply for all possible applications.
The present invention overcomes the limitations associated with existing cement additives, and presents certain advantages over the existing technology as set forth below.